In situ Absolute Calibration and Validation: A Link from Coastal to Open-Ocean Altimetry

Abstract

The determination of global and regional mean sea level variations with accuracies better than 1 mm/year is an important yet challenging problem, the resolution of which is central to the current debate on climate change and its impact on the environment. To address this, highly accurate time series from both satellite altimetry and tide gauges are needed. In both cases, the desired accuracy represents a significant challenge for the geodetic community. From the perspective of space borne altimetry, systematic errors from the orbit, reference frame and altimeter systems are all important limiting factors and must be minimized in order to derive data products of greatest geophysical value. Indeed, the objective for the overall accuracy of future altimeter systems is 1-cm (RMS) along with a stability of 1 mm/year. From the terrestrial perspective, estimating the vertical velocity of tide gauge sites to sufficient accuracy is also one of the most important and challenging problems in modern geodesy. Essential to reaching these goals in the measurement of mean sea level variation are ultra-precise validation and calibration techniques, including in situ absolute calibration experiments. Most of the present calibration experiments are on or near the coast, reinforcing the need for developing such techniques to unify the altimetric error budget for both open-ocean and local (coastal) conditions.

Keywords

Altimetry GPS In situ instrumentation Reference frame Sea level

Abbreviations

ALT-A or B

Side A or B of the TOPEX altimeter

AMR

Advanced Microwave Radiometer (OSTM/Jason-2)

Cal/val

Calibration/validation

CCAR

Colorado Centre for Astrodynamics Research

CERGA

Centre d’Etudes et de Recherches Geodynamiques et Astronomiques

CGPS

Continuous Global Positioning System

CNES

Centre National d’Étude Spatiales

CU

Colorado University

DORIS

Détermination d’Orbite et Radiopositionnement Intégrés par Satellite

ECMWF

European Centre for Medium-Range Weather Forecasts

EM

Electro Magnetic

Envisat

Environmental Satellite

ERS (1 & 2)

European Remote Sensing

EUMETSAT

European Organisation for the Exploitation of Meteorological Satellites

Notes

Acknowledgments

This chapter is dedicated to the memory of Dr. Yves Ménard for his deep involvement in the calibration and validation activities. The authors collectively acknowledge other members of their teams that have contributed to the design, operation and analyses of the calibration sites. Bass Strait: Neil White, Richard Coleman, John Church, Paul Tregoning, Jason Zhang, and Reed Burgette. Corsica: Olivier Laurain, Pierre Exertier, François Barlier, Gwénaële Jan, Yves Ménard, Claude Gaillemin, and the FTLRS team. Harvest: Ed Christensen (posthumous), George Born, Dan Kubitschek, Steve Gill, Dave Stowers, Plains Exploration and Production. A portion of this work was conducted by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA.

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